Good safety practice requires the use of a guard or other protective device on certain types of hand held power tools that because of the nature of the tool can cause serious injury to an operator contacting the tool's working member. Hand held grinding, brushing and cutting tools are known to constitute an obvious hazard. Because of this hazard numerous designs for such guards have been manufactured and provided in the past. Because the guard is only effective so long as it is in place on the tool some designs have been proposed to make the power tools inoperative should the guard be removed. One solution to this is to make the guard an integral part of the tool housing thus making removal of the guard impossible without extensive modification or substantial destruction of the tool's housing.
Other known air powered hand tools have the guard constructed to block a passageway connecting the main air inlet to the tool's driving motor. When the guard is removed air is dumped through this passageway and operation of the motor is not possible or is greatly impaired due to the leaking air. This type of guard construction requires a carefully machined surface on the guard structure to seal with appropriate mating surfaces of the tool's housing in order to insure proper operation of the power tool and prevent inadvertent leaking of the air supply.